Erica Synths DIY Eurorack Case and Power Supply Kit for EDU Modular System (84 HP) User Manual
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XS1 is a socket for the +12VDC input. XS2 is an optional socket in case you want to con-
nect several PSU boards in parallel.
VR1 is a resettable fuse – in case there’s an accidental short circuit somewhere on the
PCB or the input voltage is connected in reverse, the fuse will cut the circuit immediately.
As soon as the problem is eliminated, the fuse will automatically reset and allow for current
flow in the circuit.
VD1 is a Schottky diode that secures reverse polarity power supply protection. In this
case it works in junction with the resettable fuse VR1. Diodes pass current only in one
direction. Because the cathode of VD1 is connected to +12 V and the anode to GND, it
does not pass current through and normally it will not have any effect whatsoever on the
circuit. If a negative voltage, however, is accidentally applied to XS1, the diode starts to
conduct the current and essentially makes a short circuit between the XS1 lugs. A short
circuit means the current in the circuit tends to increase rapidly and this is where the reset-
table fuse kicks in – as soon as the current reaches 3A it breaks the circuit.
The capacitors C1-C3 serve as energy reservoirs that keep power supply voltages stable
in case there are any fluctuations in the power consumption of certain modules (e.g blink-
ing LEDs) in a modular system.
Light emitting diodes (LEDs) VD2 and VD3 are “voltage ok” indicators for both the +12V
rail (VD2) and the -12V rail (VD3). They are connected in series with current-limiting
resistors R1 and R2, respectively. LEDs are designed to operate in a certain current range
(the more current flows through an LED, the brighter it shines), but there’s certain maxi-
mum current that an LED can handle, so limiting resistors are required. The anode of VD2
is connected to the +12V rail through R1 and the cathode – to GND. If there is +12V on the
rail, a current will flow through R1 and VD2 (remember, diodes pass a current in one
direction only and the same goes for LEDs) and VD2 will light up. Same goes with the VD3
on -12V rail. If something goes wrong and there’s no 12V on the rail, the LED will be off or
half dimmed – this typically happens when modules are connected incorrectly in reverse
polarity or they are defective.
XP1-XP14 are 2x8 pin power supply connector sockets with keys to prevent reverse
polarity connection. In eurorack standard, PSU boards have 2x8 pin connectors and each
pair of pins serves a specific function. It’s described well on the modular manufacturer’s
A small schematic around DA1 is for an optional +5V power supply (parts are not
included in this kit) built around a DC linear voltage regulator (often referred to as a
low-dropout regulator or LDO) 78M05. Some eurorack modules require an external +5V
supply and as you saw from the connector pinout above, there are dedicated pins for +5V.
Our mki x es.edu modules do not require a +5V supply, therefore this part of the schemat-
ics is optional.
Now, let’s start assembling the PSU and the mki x es.edu eurorack case!